The role of Fertilization as an activator of the developmental program has only been approached inferentially in the past, not only in this meeting, but in others as well. Yet this is the link between fertilization and development, and has been the object of intense experimentation recently, with emphasis on the cellular and molecular aspects of the association. Strong parallel trends have occurred in mammalian and invertebrate systems with complementary results on the genetics, cell biology, and biochemistry of gamete interaction and its sequelae. Thus, certain aspects of fertilization appear different in different systems at the phenomenological level, but as underlying mechanisms emerge strong similarities are found. This conference will focus on the strands that this fertilization and early development together. It will concentrate on mechanisms of fertilization as they relate to activation of development and on the role of fertilization in initiating and shaping the pathway of embryogenesis. To my knowledge, no conference either in the area of fertilization or developmental biology has directed itself to this issue, using the strong parallel currents of research in invertebrate, amphibian, and mammalian systems.